A strain sensor, a sensor that senses physical changes such as tension, bending, or buckling applied to a sensor, is available for various industrial fields using the feature of sensing physical changes. Such a strain sensor could be implemented to a smart sportswear that can check the degree of relaxation and contraction of joints and muscles and the amount of exercise when a wearer takes exercise, a motion sensor that senses changes in motion of fingers and toes, and so on. Further, the strain sensor can be used in various fields from a micro-strain gauge that find out fine crack or fatigue in facilities, to a large-area strain sensor array.